Concrete walls, and other concrete structures, traditionally have been made by building a form. The forms are usually made from plywood, wood, metal and other structural members. Unhardened (i.e., plastic) concrete is poured into the space defined by opposed spaced form members. Once the concrete hardens sufficiently, although not completely, the forms are removed leaving a concrete wall, or other concrete structure or structural member in place.
Conventional removable concrete forms typically use aluminum or some type of plywood reinforced by a metal framing system. Opposed form members are held together by a plurality of metal ties that provide the form with the desired pressure rating. Conventional forms are designed to be strong, safe and durable to meet the challenges of any type of construction, residential or commercial, low-rise or high-rise, walls, columns, piers or elevated slabs.
Conventional removable concrete forms are designed to be removed once the concrete has achieved a desired strength. However, conventional removable concrete forms do not provide insulation to the concrete wall, either during concrete curing or after removal. Consequently, as the concrete is setting and the hydration process is beginning the concrete internal temperature rises to a first peak temperature while at the same time heat is continuously lost to the environment through the un-insulated concrete form panels. Then, generally overnight, as the ambient temperature drops, the concrete cools at a very rapid pace. This rapid cooling creates temperature shock and leads to thermal shrinkage that causes what the industry refers to as concrete temperature shrinkage cracking. After the initial heat loss, as the ambient temperature rises on the following day, the conventional un-insulated concrete forms absorb heat from the environment and the concrete temperature rises to a second peak temperature, which is lower than the first peak temperature, and as the ambient temperature again drops overnight, the concrete heat is once again lost to the environment through the un-insulated concrete form. This process continues from day-to-day following the diurnal temperature swings. Such diurnal temperature fluctuations place thermal stresses on the concrete at a time when the concrete tensile strength is lower than the thermal stresses which allows the initial temperature shrinkage cracking to proliferate. Sulfates, salts and moisture penetrate cracked concrete faster than dense and non-cracked concrete. Through the cracks, moisture and salt prematurely reach steel reinforcement which cause corrosion. Over time, this is a leading cause of concrete failure.
Conventional practice sometimes places insulated blankets over the exterior of the concrete forms to prevent concrete freezing. However, such insulated blankets are relatively thin and are not designed or effective to retain the heat of hydration within the concrete formwork. Also, since concrete forms are usually removed after a relatively short time after concrete placement, insulated blankets are usually removed as well. Although insulated blankets are sometimes used to wrap the concrete after the forms have been removed, such practice is inefficient and doubles cost of installation.
In mass concrete placement using conventional un-insulated concrete forms, while the concrete gains heat at the core, the concrete surface which is in contact with the concrete form loses heat to the surroundings based on the diurnal temperature fluctuations mentioned above further increasing the thermal stresses from the core to the concrete surface. While insulated blankets are sometimes used to wrap mass concrete, the amount of insulation provided by such insulated blankets is relatively low and is only provided to reduce the temperature differential between the surface and the core.
It would therefore be desirable to provide a concrete form that reduces the loss of the heat of hydration to such an extent that thermal shock and stresses are reduced or eliminated and as a result concrete cracking is reduced. By retaining the heat of hydration for longer periods of time, the density of the concrete is increased and the early strength of the concrete is improved. However, for certain applications it may not be desirable to have insulation permanently attached to the concrete. Furthermore, leaving the insulation permanently attached to the concrete is more expensive than using conventional removable concrete forms. Additionally, in order to retain the heat of hydration more economically, it would be desirable to make the insulated concrete form removable and reusable.
It is also desirable to monitor the temperature of the curing concrete in either a removable concrete form, an insulated concrete form or a removable insulated compound concrete form, as disclosed in the present invention. In the prior art, wireless temperature sensors include both a processor/transmitter portion and a temperature sensor portion; i.e., thermocouple. In the prior art, both the processor/transmitter portion and the temperature sensor portion are embedded in the cured concrete, and, therefore, cannot be reused. This makes monitoring the temperature of curing concrete relatively costly. Therefore, it would be desirable to provide a curing concrete temperature monitoring system that is more economical than prior art systems.